Who can you trust? That’s the gamble, and when it comes to choosing a partner, fidelity is a core aspect most of us require.

Yet the adage, “once a cheater, always a cheater,” isn’t always true. Here are five guidelines you can use right now to make the wisest choice before dating someone who's cheated.

1. Weigh their past

Factually, odds are highest that your sweetie will treat your relationship boundaries like they treated those boundaries in other relationships. In study after study, past behavior is your crystal ball; it’s the single best predictor of how any of us will behave, given similar circumstances. It’s one reason why someone who cheated with you is likely to cheat on you.

Overlook this rule of thumb, and you’ll get hurt again and again. People tend to do what and whom they have done before.

2. Note their timing

The recent past is particularly important. How long ago was the affair? A person who cheated last month and says it won’t happen again might be telling the truth. But the person who had an affair once, ten years ago, and never did it again, is far safer.

Timing also matters in the context of their former relationship. Most people, including people who have had an affair, aren’t willful philanderers. But a statistically small group sees “getting some” — strange as that is — as their right. If they’ve cheated early in the passionate love phase of a relationship–during serious exclusive dating, engagement, or in the honeymoon phase of marriage—that’s a red flag you’re with one of them.

3. Examine their habits

Was their cheating a one-night, one-time thing, or something they turned to often? Repeated acts are likelier to recur; they become habits. And especially in stressful times, people return to their habits.

All relationships go through stresses. Are you okay with a partner whose default is soothing themselves in another’s arms?

4. Explore their insight

What reasons does your new love give for their past infidelity? Do they offer excuses — or remorse? Do they give themselves a pass–or did they commit to change even if they were never caught, because in their view, affairs are wrong and they don’t want to catch themselves violating their own moral code? Do they accept responsibility for their choices and behavior, or do they pawn it off on their ex’s failings?

It’s a safer bet for you if your would-be mate takes it all on the chin: my fault, my responsibility, and my choices led to this. Remember the saying, the first step to change is knowing you have a problem? Ownership is key. If your date defends, excuses, and finds just cause for their past infidelity, prepare for more.

Bonus points if they acknowledge a basic moral code of fidelity. A person who uses rough times in the relationship or flaws in their ex as an excuse for infidelity is a person who most likely will be unfaithful again.

5. Consider yourself

During prep for this article, I heard from many people who basically said, “Even if you gave me all the data on best-cases, I would never again date someone who cheated. A partner was unfaithful to me, and I would always be waiting for the other shoe to drop.” Or, “I trusted someone with a past, and they cheated on me too.”

If that’s you, the psychological strain is just not worth it. Under those circumstances, it’s likely best to avoid everyone with a history of infidelity, no matter what might indicate it wouldn’t recur. Living with constant fear is contrary to loving yourself, and besides, most people have never cheated on anyone. Choose from among them!

So, who can you trust? You can trust everyone — to be who they already are. Take a clear-eyed view of your partner; accept that you aren’t going to change them; weigh the available evidence; and get honest about your own comfort level. You have the tools you need.

Then — trust accordingly. It’s not a guarantee. Science has few of those. But it’s the way to bet.

Dr. Duana Welch is a relationship coach and the author of Love Factually, the first book that uses science rather than opinion to help men and women put all the odds in their favor for every stage of dating. You can get a free chapter and learn more at http://www.lovefactually.co/